Approximately 20% of college students are regular marijuana users, and are at risk for cognitive and academic problems, addiction, and risk behaviors such as driving while impaired. Young adult marijuana users are thus a high-risk population and may require an intervention that motivates marijuana reductions by increasing engagement in constructive alternatives to marijuana use. Brief Motivational Interventions (BMIS) have demonstrated efficacy for alcohol use in college students, but lack consistent evidence of efficacy for marijuana use. This research team has developed a supplement to alcohol BMIs, the Substance-Free Activity Session (SFAS), which directly targets the behavioral economic mechanisms of both substance-free reinforcement and delayed reward discounting by encouraging the development of and commitment to academic and career goals, and by highlighting the impact of day-to-day patterns of alcohol use and academic engagement on these goals. A controlled pilot trial found that the SFAS improved BMI outcomes in a sample of heavy drinking college students, and the ongoing parent trial to this revision is replicating and extending those results. The proposed (two-year) Collaborative Research on Addiction Competitive Revision would evaluate the SFAS using a randomized 3-group (BMI + SFAS vs. BMI + Relaxation Attention Control, vs. Assessment Only) pilot trial with 120 undergraduates (50% female, 40% minority) who report using marijuana on > 4 days in the past-month. The results would extend the aims of the parent grant by determining whether the SFAS enhances the efficacy of a standard marijuana BMI, and provide effect size estimates that would guide the development of a larger trial. It is hypothesized that at the 1-month and the next-semester follow-ups (follow-ups are wedded to the academic calendar to allow for representative measurement of marijuana use and activity patterns) BMI+SFAS participants will report significantly lower levels of marijuana use and problems, and that these reductions will exceed those of BMI + Relaxation and Assessment-Only participants. Exploratory analyses will test the hypotheses that (a) the BMI + SFAS will be more effective for participants who report higher baseline marijuana reinforcing efficacy and delayed reward discounting; and (b) the advantage of BMI + SFAS on marijuana use will be mediated by increased participation in substance-free activities. Support for our hypotheses would extend behavioral economic theory and would provide initial validation for an approach that could be used to reduce marijuana misuse among the increasing population of college students who misuse marijuana. Furthermore, given the focus of the SFAS is to increase academic/campus engagement, this work has the potential for widespread dissemination.